Why can we characteristic properties of a substance to identify it

We can characterize properties of a substance to identify it because it helps us determine how the substance should be used. We can identify a substance by using physical or chemical properties. These help us by telling us which chemical we are looking at.  

I hope this helps.. I wasn't sure what kind of answer you were looking for.

Most smaller stars don't have a radiative zone.

Particle exchange energy though elastic collision , hope this .